The present invention relates to a variable valve type internal combustion engine and a control method used in vehicles such as automobiles, and particularly to a variable valve type internal combustion engine and a control method in which the intake airflow is controlled by continuously controlling the lift amount and the open valve period of the intake valve.
Recently, a variable valve type internal combustion engine is spreading for the decrease in the fuel consumption of the automobile engine, in which the intake airflow is controlled with the intake valve which can set the lift amount and the open valve period in changeability. Such a variable valve type internal combustion engine has two intake ports in one cylinder, and an intake valve which individually opens and shuts each intake port. In a low revolution region of the internal combustion engine, one intake valve is fixed in a closed state regardless of the height of the engine load, and at least one of the lift amount and the open valve period of the other intake valve is gradually increased to control the air amount as the load of the engine increases. At the same time, the swirl control is performed in the combustion chamber. (For instance, Japanese Patent Application Laid-Open No. 7-332045).
It is thought that the intake airflow is insufficient in the low revolution number and the high load region because a part of intake valves is stopped in the engine low revolution number operation region in the conventional variable valve type internal combustion engine described in Japanese Patent Application Laid-Open No. 7-332045.
Moreover, it is not considered to decrease the variation of the intake airflow due to the variation (error) of the lift amount and the open valve period of the intake valve in the low intake airflow region in the conventional variable valve type internal combustion engine. The variation of the intake airflow, especially the variation of the intake airflow in the low intake airflow region decreases extremely the control accuracy of the air fuel ratio of the mixture (fuel-air), and deteriorates the performance of an engine.